Heat-sensitive copying sheet



Dec. 28, 1965 D. SMITH ETAL 3,226,288

EEEEEEEEEEEEEEEEEEEEEEEE ET Filed Jan. 24, 1962 POROUS PA ER SHEET WAX LAYER 6,455 SHEET United States Patent 3,226,288 HEAT-SENSITIVE COPYING SHEET Daniel Smith, Riverdale, and Edward C. Otto, Brooklyn,

N.Y., Donald J. Lazzarini, North Bergen, Null and John F. McHngh, Brooklyn, N.Y., assignors to interchemical Corporation, New York, N.Y., a corporation of Ohio Filed .lan. 24, 1962, Ser. No. 168,534 19 Ciaims. (Cl. 161-229) This invention relates to copy sheets and to a method of making copies therewith. More particularly the invention relates to copy sheets for use in making copies by a thermographic technique wherein the image on the copy sheet is the result of a physical change produced by localized heating in the image area.

In recent years thermocopying of typed or printed originals has become increasingly popular. T hermocopying involves placing the original in heat conductive relationship with a sheet of copy paper and then subjecting the original and copy sheet to intense irradiation of such character that the printed or typed matter on the original absorbs at least a portion of the radiant energy thereby converting it into heat which causes the image of the original to be developed in the copy sheet. In such a process it is apparent that the copy sheet must be constructed in such manner as to be capable of changing to a contrasting color when heated. The thermocopying process and machines for carrying out the process and certain types of heat-sensitive papers are described in numerous prior art patents, for instance, United States Patents 2,663,654-7; 2,710,263; 2,740,895-6. In the prior art, the heat-induced image formation on the copy sheet may be caused by chemical reaction, usually to produce a dark colored image on a lighter background, or image formation may result from a physical change. In the latter type, the image formation may result from the transparentization of a fusible opaque coating or bytransparentization of an opaque blushed lacquer coating to show a dark background or a background of contrasting color.

The present invention provides still another type of heat-sensitive copy sheet for use in the thermocopying process. In accordance with the invention, a base sheet, preferably a substantially non-oil-absorbent sheet, is provided with a layer of a normally solid, organic composition which becomes a fluid of relatively low viscosity at a melting point preferably from about 60 to 150 C. The base sheet in combination with the layer should provide a structure having a surface of a dark color. This may be accomplished either by the combination of a base sheet of a dark color and a colorless transparent layer or by the incorporation of coloring matter into the layer.

Over the layer, there is adhered a sheet of porous absorbent fibrous material of suliicient opacity to substantially mask the color of the colored structure. When such a sheet is properly exposed in the thermocopying process, an image is formed by migration of the molten organic material in the image areas into the sheet of porous fibrous material, e.g., Where the organic layer is colorless and transparent, the molten material transparentizes the upper sheet, thereby permitting the dark base sheet to show through. On the other hand where the layer contains coloring matter, the molten organic composition carries said coloring matter into the sheet of porous fibrous material.

Such a heat-sensitive copy sheet has many advantages. For instance, it is substantially non-pressure sensitive whereas heat-sensitive papers made heretofore, using the opaque blushed lacquer technique or the fusible opaque coating technique, have considerable objectionable pressure sensitivity. While prior art chemical reaction types 3,226,288 Patented Dec. 28, 1965 of heat-sensitive papers are not pressure sensitive, they do have other disadvantages, such as the tendency to become brittle on aging or the tendency, also on aging, to lose image contrast due to the darkening of the non-image areas. The heat-sensitive sheet of the present invention does not become brittle with aging. Thus, the invention is a great advance in the art in that it provides a heatsensitive paper that is non-pressure sensitive but still does not become brittle or lose contrast on aging. Further advantages of the invention will be apparent from the following detailed description and claims in which all proportions are by weight unless otherwise stated.

The base sheet of the new copy sheet should preferably be substantially less porous and less absorbent than the top sheet so as to avoid strikethrough of the colored organic layer to give a discolored back to the composite sheet, to avoid having an image appear on the back sheet at the same time the desired image is developed on the top sheet and to avoid the loss, by migration into the base sheet, of organic material necessary to provide the image on the top sheet.

A copy sheet that is relatively transparent to infrared radiation is preferred since infra-red is the most effective radiation for use in thermocopying. Where the sheet is to be used for front copying it is, of course, essential that the paper be substantially transparent to the strong radiation used to develop the copies, that is. the top sheet, organic layer, base sheet and any coloring matter used must be infra-red transparent. If the sheet is to be used only for back copying the paper need not be transparent because in the back copying technique the radiation does not pass through the copy sheet.

In order to secure optimum migration of the molten organic material into the top sheet, said sheet should preferably have a porosity (as measured on the Gurley DensometerMethod A of ASTM D726-58) not greater than 16 seconds for the passage of air through one square inch of sheet. Furthermore, in order that the color of the under structure will not show through, the top sheet should have an opacity of at least 60% (as measured on an Emil Greiner Tester in accordance with ASTM D48944). In addition, the top sheet should have a high oil absorbency. Oil absorbency may be measured by a simple test. A drop of oleic acid having dissolved therein any suitable dye is placed on one surface of a sheet and the amount of time required for the drop to penetrate through to the other surface of the sheet is measured. The top sheet preferably has an absorbency such that the oleic acid penetrates through to the other surface in less than 1 second and most preferably less than 0.5 second.

It has been found that a top sheet having the above properties may be made of paper comprises of short cellulose fibers substantially all of which are less than 1 mm. in length. The top sheet has a color, preferably white, which will provide the maximum contrast with the colored organic composition in the intermediate layer.

In order to enhance the opacity and whiteness of the top sheet, it may contain any of the conventional mineral pigments or fillers used in paper, e.g., clay. The top sheet is preferably from 0.5 to 2 mils in thickness.

The base sheet, as has been set forth above, has a porosity and oil absorbency preferably substantially less than that of the top sheet. In fact, the oil absorbency of the base sheet should be very low. It should be sufficiently low so that the intermediate layer which is applied in the molten state has time to solidify before there is any danger of the material of said layer penetrating through said sheet. Using the previous oleic acid penetration test, preferably the drop should not penetrate the base sheet in less than five seconds. The base sheet may be made of a wide variety of materials, e.g., 5 lbs. to 9 lbs. white bond paper, Mylar (polyethylene terephthalate), 20 lbs. glassine, cellulose acetate and supercalendered cigarette tissue. The base sheet is preferably from 0.5 to 2 mils in thickness.

In accordance with one aspect of this invention an excellent thermosensitive copying sheet is provided when the intermediate layer of the laminate comprises a waxy material preferably having a melting point of from 80 C. to 150 C. and most preferably from 88 C. to 110 C.

The Wax intermediate layer may comprise mineral waxes, e.g., carnauba, candelilla. For best results microcrystalline waxes, particularly microcrystalline waxes having a melting point between 88 C. and 105 C. are preferred. The Waxes are preferably colored by the incorporation of a conventional dye. Since the top sheets are preferably white, the waxy material is advantageously dyed a dark color. Methyl violet and solvent black dyes have been found to give good results.

While the laminate having the waxy intermediate layer displays good adherence, said adherence may be even further improved by the incorporation of an additive to the waxy material which increases the adhesiveness of said waxy material. Additives which are compatible with the wax when said wax is in the molten state but which are incompatible with said wax in the solid state are preferred. Such additives include Abitol which is a technical grade hydroabietyl alcohol, Aroclor 4465, which is 75:25 parts chlorinated biphenylszchlorinated triphenyls with a chlorine content of 65%, and, alternatively, polymethylstyrene. The additive preferably comprises from 10 to 30% of the total waxy composition weight.

The layer of waxy material is preferably applied to the base sheet in the molten state with conventional coating equipment. This may be accomplished by the hotmelt method using a Mayer coater. Then the top sheet is laminated onto the coated surface of the base sheet at a temperature below the melting point of the wax, conveniently at room temperature.

Polyamide resins having a melting point between 60 and 120 C. have been found also to provide good compositions for the intermediate layer of the laminates. Suitable polyamide resins include Versamide polyamides made in accordance with US. Patent No. 2,379,413 as well as polyamides produced by the condensation polymerization of diamines e.g., ethylene diamine with the reaction product of tung oil fatty acids and acrylic acid.

It has been previously mentioned that the organic composition of the intermediate layer should melt to a low viscosity fluid. It is preferable that this fluid have a viscosity below 1000 centipoises and most preferably below 300 centipoises. Thus in the case of polyamide resins where the molten viscosity is higher than desired, additives may be incorporated into the polyamide composition to reduce molten viscosity. Higher alkanols such as cetyl and stearyl alcohol have been found to be very desirable for this purpose. Other additives which reduce the viscosity of polyamides include carbowaxes, castor wax as well as long chain amides of fatty acids such as Armid HT comprising 22% hexadecanamide, 75% octadecanamide, and 3% 9-octadecenamide; Armid C comprising 8% octanamide, 7% decanamide, 49% dodecanamide, 17% tetradecanamide, 9% hexadecanamide, 2% octadecanamide, 6% 9-octadecenamide and 2% 9,12-octadecadiene amide; and Armid comprising 6% octadecanamide, 9% 9-octadecenamide and 3% 9,12- octadecadiene amide. Like the application of the waxy composition it is preferable to apply the intermediate layers to the base sheet by hot-melt coating.

It has been further found that organic compositions having crystalline characteristics which melt in the range of 60 to 120 C. may be used to provide the low viscosity component which migrates into the top sheet. Such organic compositions include resorcinol, acenaphtheme and parahydroxyacetophenone. Where such organic compositions do not have the necessary adhesion to bond the top and base sheets, it is necessary to further include in said intermediate layer a binder. Such binders preferably include a resin for support and where the resin lacks sufiicient adhesiveness an additive to improve adhesion of the binder, e.g., suitable binder compositions are polystyrene resin and poly-a-methyl styrene as well as polyvinyl chloride-acetate resins and tricresyl phosphate. Preferably the crystalline organic composition is not soluble in the binder. It is most preferable under these circumstances to apply the organic composition to the base sheet as a dispersion in a voltatile organic solvent solution of said binder. The solvent used for said binder should not be a solvent for said organic composition. Where coloring matter is used in such dispersion, it is preferable that the coloring matter also be insoluble in the solvent. Further, it is preferable that the binder be infusible within the heat range to which the copying sheet is to be exposed e.g. within 60 to 120 C.

In the product of this invention the dye preferably comprises from 1 to 10% of the total weight of the organic composition. The intermediate layer is preferably from 0.1 to 0.8 mil in thickness and most preferably from 0.2 to 0.5 mil in thickness.

The drawing is a schematic illustration of the copying sheet of this invention.

The following examples will further illustrate this invention:

Example 1 A mixture of parts of a microcrystalline wax having a melting point of 88-91 C. (ASTM Dl2730) and a viscosity of less than 300 cps. when melted and 10 parts of methyl violet dye is hot-melt coated at 110 C. and at a thickness of 0.3 mil onto one surface of an infra-red transparent 4.5 lb. White Washington paper (Schweitzer Paper Co.). There is then laminated onto the coated surface of said paper, a 4 lb. infra-red transparent white tissue paper having an oil absorbency of less than 0.5 second for a drop of oleic acid, an opacity of greater than 60% (ASTM-D589-44) and a porosity (measured by the Gurley Densometer) such that cc. of air passed through one square inch of paper in not more than 16 seconds (Method A of ASTM D726- 58), substantially all of the fibers of said paper having a length of less than 1 mm. The lamination is carried out at room temperature by conventional means, e.g., cold rollers. The heat-sensitive papers produced may be used to produce copies by the front and back printing techniques in the Thermo-Fax Copying Machine. Such temperatures as are obtainable in the lower heat ranges of said copying machine which ranges are preferred.

Example 2 Example 1 is repeated using the same materials and conditions except that the coating composition comprises a mixture of 98 parts of microcrystalline Wax having a melting point of from 91 to 93 C. and 2 parts of solvent black dye. The resulting heat-sensitive copying paper has similar properties to that of Example 1.

Example 3 Example 1 is repeated using the same material and conditions except that the coating composition comprises a mixture of 40 parts of yellow carnauba wax, 30 parts of ozocerite wax, 10 parts of methyl violet dye and 20 parts of Bareco Superbond #10 (a microcrystalline wax composition). The resulting heat-sensitive copying paper has similar properties to that of Example 1.

Example 4 Example 1 is repeated using the same materials and conditions except that the coating composition contains a mixture of 78 parts of microcrystalline wax having a melting point of from 91 to 93 C., 2 parts of solvent black dye and 20 parts Abitol, a technical grade hydroabietyl alcohol comprising 45% tetrahydroabietyl alcohol, 40% dihydroabietyl alcohol and 15% dehydroabietyl alcohol. The resulting heat-sensitive copying paper has similar properties to that of Example 1 except that it displays improved laminate adhesion.

Example 5 Example 1 is repeated using the same materials and conditions except that the coating composition contains a mixture of 88 parts of microcrystalline wax having a melting point of 91 to 93 C., 2 parts of solvent black dye and parts of Dow Resin 276V2, poly-alpha-methylstyrene and the coating thickness is 0.2 mil. The resulting copying paper has similar properties to that of Example 1 except that it displays improved laminate adhesion.

Example 6 A polyamide resin is prepared by heating a mixture of 500 g. of tung oil fatty acids, 130 g. of acrylic acid and 2 g. of hydrokuinone to 130 C. under an N atmosphere for 6 hours. Excess acrylic acid is then removed by vacuum stripping. 317 g. of the product and 59.3 g. of ethylene diamine are heated for 11 hours under an inert atmosphere at 200 C. Any water formed is removed overhead. The product has an acid number of 7.

The product is then hot-melt coated at 132 C. and at a thickness of 0.3 mil onto one surface of an infra-red transparent black sheet conventionally used in making carbon paper. There is then laminated onto the coated surface of said paper, a 4 lb. infra-red transparent white tissue paper having an opacity of greater than 60% (ASTM D589-44), an oil absorbency of less than 0.5 second for a drop of oleic and a porosity (measured by the Gurley Densometer) such that 100 cc. of air passed through one square inch of paper in not more than 16 seconds (Method A of ASTM D726-58), substantially all of the fibers of said paper having a length of less than 1 mm. The lamination is carried out at room temperature by conventional means, e.g., cold rollers. The heat-sensitive papers produced may be used to produce copies by the front and back printing techniques in the Thermo-Fax Copying Machine. Such temperatures are obtainable in the lower heat range of said copying machine which ranges are preferred.

Example 7 Example 6 is repeated except that instead of the polyamide of Example 6, a polyamide produced by the condensation of dilinolenic acid and ethylene diamine in accordance with the procedure described in US. Patent No. 2,379,413 having a softening point (ASTM E28- 5lT) of from 105 to 115 C. mixed with stearyl alcohol is used for the hot-melt coating in a ratio of 75:25 polyamide:alcohol. The resulting heat-sensitive copying paper has similar properties to that of Example 6.

Example 8 Example 8 is repeated using the same reactants, proportions and conditions except that acenaphthene is used in place of resorcinol.

The resulting film is tacky and- Example 10 Example 8 is repeated using the same reactants, proportions and conditions except that parahydroxyacetophenone is used in place of resorcinol.

While there have been described what is at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A thermosensitive copying sheet which includes a base sheet coated with a layer comprising a normally solid organic composition which melts to a low viscosity fluid at a melting point from 60 to 150 C., said layer having laminated thereto an upper sheet of paper having an opacity of at least 60% and a porosity such that a maximum time of 16 seconds is required for the passage of cc. of air through an area of one square inch of the upper sheet as determined by ASTM D72658, Method A.

2. The thermosensitive copying sheet defined in claim 1, wherein the base sheet is dark colored, the upper sheet has a contrasting color and the layer is transparent.

3. The thermosensitive copying sheet defined in claim 1, wherein the layer further comprises dark coloring matter which is soluble in said organic composition and said upper sheet has a color contrasting with said colored layer.

4. A thermosensitive copying sheet which includes a base sheet coated with a layer of a dark colored, normally solid, wax composition which becomes a fluid of relatively low viscosity at its melting temperature, said wax layer having laminated thereto an upper sheet of paper of a contrasting color having an opacity of at least 60% and a porosity such that a maximum time of 16 seconds is required for the passage of 100 cc. of air through an area of one square inch of the upper sheet as determined by ASTM D72658, Method A.

5. A thermosensitive copying sheet as defined in claim 4 in which the colored wax layer comprises colored microcrystalline wax having a melting point of 88 C. to C.

6. The thermosensitive copying sheet defined in claim 4, wherein said wax material comprises up to 30% hydroabietyl alcohol and the remainder microcrystalline Wax having a melting point of from 88 C. to 105 C.

7. The thermosensitive copying sheet defined in claim 4, wherein said wax material comprises up to 30% of polyalpha-methylstyrene and the remainder microcrystalline wax having a melting point of from 88 C. to 105 C.

8. The thermosensitive copying sheet defined in claim 3, wherein said organic composition is resorcinol and said layer further contains polystyrene.

9. The thermosensitive copying sheet defined in claim 3, wherein said organic composition is acenaphthene and said layer further contains polystyrene.

10. The thermosensitive copying sheet defined in claim 3, wherein said organic composition is parahydroxyacetophenone and said layer further contains polystyrene.

11. The thermosensitive copying sheet defined in claim 1, wherein said organic composition is a polyamide resin.

12. The thermosensitive copying sheet defined in claim 11, wherein said poyamide is the polymerization product of ethylene diamine with the reaction product of acrylic acid and t-ung oil fatty acid.

13. The thermosensitive copying sheet defined in claim 11, wherein said polyamide is the condensation polymeri zation product of dilinolenic acid and ethylene diamine.

14. The thermosensitive copying sheet defined in claim 13, wherein said layer further contains an .alkanol of from 16 to 18 carbons.

15. A thermosensitive copying sheet as defined in claim 1, in which the upper sheet is a mineral pigment filled paper sheet composed of short cellulose fibers.

16. The thermosensitive copying sheet defined in claim 19 The thermosensitive copying sheet defined in claim 3, in which said base sheet, layer, coloring matter and top 1, wherein the base sheet is less absorbent than the sheet are infra-red transparent. upper sheet.

17. The thermosensitive copying sheet defined in claim 1, wherein the thickness of said layer is from 0.8 to 5 References Clted y the Exflmlllel 1 th t h td fi d 1 UNITED STATES PATENTS ermosensl We Copymg S 6 C 565 043 8/1896 Stockhouse 101 12s.2

1, wherein the upper sheet has an 011 absorbency such 3,109,748 11/1963 Newman 117 367 that a drop of oleic acid applied to one surface thereof wilsleaterrligtrate through to the other surface in less than 10 ALEXANDER WYMAN Primary Examiner. 

1. A THERMOSENSITIVE COPYING SHEET WHCH INCLUDES A BASE SHEET COATED WITH A LAYER COMPRISING A NORMALLY SOLID ORGANIC COMPOSITION WHICH MELTS TO A LOW VISCOSITY FLUID AT A MELTING POINT FROM 60* TO 150*C., SAID LAYER HAVING LAMINATED THERETO AN UPPER SHEET OF PAPER HAVING AN OPACITY OF AT LEAST 60% AND A POROSITY SUCH THAT A MAXIMUM TIME OF 16 SECONDS IS REQUIRED FOR THE PASSAGE OF 100 CC. OF AIR THROUGH AN AREA OF ONE SQUARE INCH OF THE UPPER SHEET AS DETERMINED BY ASTM D726-58, METHOD A.
 11. THE THERMOSENSITIVE COPYING SHEET DEFINED IN CLAIM 1, WHEREIN SAID ORGANIC COMPOSITION IS A POLYAMIDE RESIN.
 12. THE TERMOSENSITIVE COPYING SHEET DEFINED IN CLAIM 11, WHEREIN SAID POLYAMIDE IS THE POLYMERIZATION PRODUCT OF ETHYLENE DIAMINE WITH THE REACTION PRODUCT OF ACRYLIC ACID AND TUNG OIL FATTY ACID. 